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The influence of torrefaction temperature on the durability, combustion characteristics, and emissions of CO, CO2, NOX, and particulate matter (PM) from biomass pellets was studied. The pellets were torrefied under inert conditions at 225, 250, and 300 °C for 60 min. Physical properties, such as weight loss, fines percentage, pellet durability index (PDI), and water absorption, were evaluated using ISO standards. The weight loss increased with higher torrefaction temperatures. Torrefied pellets had lower water absorption than untreated pellets. Fines percentage increased with torrefaction temperature while PDI decreased. Torrefied pellets at 300 °C had the lowest PDI (82.7%), while 225 °C had the highest (98.0%). The energy density and heating values increased with torrefaction temperature from 22.0 MJ/kg at 225 °C to 29.9 MJ/kg at 300 °C compared to 18.9 MJ/kg for untorrefied pellets. There were reductions in CO, CO2, and NOX emissions with an increase in torrefaction temperature while PM slightly reduced. This study found that torrefied biomass pellets had lower CO2 emissions than raw pellets.

Torrefaction of selected wood samples of Pinus Carrebea and Leucaena Leucocephala were carried out at temperatures ranging from 200 to 300°C to improve the energy parameters of biomass and to determine the effect of torrefication temperature on the physical and combustion properties of wood selected from Pinus carrebea and Leuceanea leucocephala grown in Nigeria. In this process the biomass hemicellulose is degraded, maintaining its cellulose and lignin content. The samples were dried and heated to 225, 250, 275, and 300°C. Then the torrefied mass was subjected to basic property testing on proximate analysis and heating value was calculated in order to understand the differences between raw material and its torrefied products. Specifically, the wood blocks changed from light brown to black, stemming from the partial carbonization at the wood surface. When the temperature is 225°C, the color of the wood is between dark brown and once the torrefaction temperatures are 250 and 275°C, the colors of the wood become dark and darker respectively. The results of the proximate analysis also showed that increasing of torrefied temperature; volatile fraction was reduced while fixed carbon was increased with increase in temperature from 21.34 to 52.74 and 18.58 to 56.83 for Leucaena leucocephala and Pinus carreabeanus respectively at 225 to 300°C. The volatile content is decreased from 78.58% to 62.76% with increase in temperature. Ash content of were within 1.57-3.41% of torrefied wood. It could be observed that the High calorific value (HCV for pine ranged between 19.80 and 28.06MJ/Kg for the top, 19.93and 24.96MJ/kg for middle with 19.72and 25.96MJ/Kg for base. The values recorded for raw sample and at 275°C been the lowest and highest respectively. The High calorific value (HCV) were found to be on the increase and nose dive at 300°C for the tree parts used in this research. The result revealed that for Leuceana the value increased from raw up to 275°C and at 300°C, a drop in the HHC was experienced. The result also showed that between raw and 250°C the value were statistically not at variance though higher value was recorded at 250°C (22.04MJ/kg). Likewise, between 275°C and 300°C there was no variance statistically, but higher value was observed for 275°C (26.32). It could be observed that the HHC for pine ranged between 19.80 and 28.06MJ/Kg for the top, 19.93 and 24.96MJ/kg for middle with 19.72 and 25.96MJ/Kg for base. The result also showed that between raw and 250 the value were statistically not at variance though higher value was recorded at 250 (22.04MJ/Kg). Likewise, between 275°C and 300°C there was no variance statistically, but higher value was observed for 275°C (26.32MJ/Kg). The proximate analyses revealed that the species are a suitable biomass source for torrefaction process and calorific value increase compared to control raw sample.